In their development of onshore gas fields in South Texas Shell has encountered margins in which the difference between dynamic ECD and static BHP is the difference between lost circulation and influx. Their solution to eliminate those problems included liner drilling and automated MPD. Those complementary technologies allowed Shell to extend static underbalanced drilling to extremely tight margins, eliminate losses and stuck pipe, and manage constant BHP during periods of high drill gas and cementing operations.
An automated and modular MPD system was recently used in two wells to hold constant BHP in a very narrow window without a back pressure pump. In the first well, Shell used the system to drill-in 740 ft of 7-5/8” liner in an 8-1/2” hole with 15.0 ppg mud statically underbalanced relative to wellbore stability. In the second, the system was used to drill-in 700’ of 3-1/2” tubing in a 6-1/2” hole with a static mud of 15.7 and a dynamic ECD of 16.2 ppg. In that interval the upper limit was estimated to be a 16.5 ppg fracture gradient and the lower limit, a 15.8 ppg pore pressure.
In the second well the level of drill gas rose to over 1400 units. However, even with such high levels of gas the new MPD system was able to maintain the BHP between +/− 0.2 ppg while making connections and trapping gas in the annulus. Shell was able to avoid the cost of a contingency 5-1/2” liner drilling operation and for the first time used an automated MPD system to manage constant BHP while cementing a drilled-in production tubing string.
The small footprint and improved control capability of the new MPD system can provide onshore and offshore operators an efficient solution to improve drilling and cementing operations in mature depleted fields.